The present invention relates generally to the remote power control of electronic devices in a computer system.
In modern computer systems, mass storage devices such as disk arrays, tape drives etc. are often packaged in one or more separate enclosures, with each enclosure having its own separate power supply. These separate enclosures are connected to the main processor of the computer using a parallel bus such as SCSI or a serial link employing a communication protocol such as the Serial Storage Architecture (SSA) or FiberChannel (FC-AL).
In such systems, it is desirable to have a way to remotely control the power of these separate enclosures from the main processor, so that in effect the whole computer can be turned on or off at a single switch. In the past, this has been achieved by use of an additional connection from the processor to the enclosures, using RS232, Ethernet or some other signalling protocol. This technique is referred to as out of band signalling. However installing this additional connection can be difficult or expensive, particularly where the enclosures are at considerable distance from the processor.
In computer systems of the type shown in FIG. 1, in which the device enclosures 20 are each connected to the main processor 10 by means, for example, of a SCSI bus 30, it is possible to use in-band signalling for remote power control of the enclosures. In particular the TERMPOWER line of the SCSI bus is driven by the host system and can be sensed by each enclosure, independent of any other enclosure. Thus remote power control is achieved by each enclosure sensing the TERMPOWER line which is powered if the main processor is powered. When the main processor power is shutdown, each enclosure detects the change in the TERMPOWER line and shuts itself down.
In-band signalling of this type is not possible in systems where the main processor is not separately connected to each of the enclosures. In such cases, the main processor is connected to a first enclosure which is in turn connected to a second enclosure and so on. The main processor cannot signal in-band to the second enclosure if the first enclosure is not powered.
It would be desirable to find a way to provide in-band remote power control of devices in a computer system where each device communicates only with adjacent devices.
According to a first aspect of the invention there is provided a method of providing remote power control of electronic devices connected for communication with at least one controlling data processing system by means of a link configured as a chain, each device including one or more ports for receiving signals over the link; the method including the steps of: issuing a shutdown command from the controlling data processing system to selected devices over the link; in response to the receipt of a shutdown command at a device, causing the device to enter a standby mode on cessation of signal activity at any of the one or more device ports; on entering standby mode at a device, supplying standby power in the device to allow the device to monitor the one or more device ports for incoming signals and ceasing transmission of signals via the one or more ports; and on receipt of a signal at any of the one or more ports that was previously inactive, restoring power to the device.
According to a further aspect of the invention there is provided an electronic device including: one or more ports for connecting the device onto a link to enable the device to communicate with a controlling data processing system; means for monitoring signal activity at the one or more ports; power control means responsive to the receipt of a shutdown command issued over the link by a connected controlling data processing system, to cause the device to power down on cessation of signal activity at one of the device ports; and auxiliary power means for supplying power to the signal monitoring means when the device is powered-down, the power control means restoring main power to the device on receipt of a signal at a port that was previously inactive.
Thus the present invention makes use of a shutdown command that causes those devices to which the command is addressed to enter a low power standby mode on cessation of signal activity on any device port. A command is employed in the present invention because an enclosure should not normally power down if a single incoming signal disappears.
Where the device is directly connected to the controlling data processing system, it will almost invariably be the case that it is the cessation of signal activity on the device port connected to the xe2x80x98upstreamxe2x80x99 controlling processing system that causes the device to enter the standby mode. It is likely that at this point, the device port connected to a xe2x80x98downstreamxe2x80x99 device will still be active.
When the device enters its low power standby mode, it ceases transmission of signals on all of its communication ports, causing other devices in the chain to power-off provided they too have received a shutdown command. Thus each device in the chain is powered off in turn. On entry into standby mode, this causes the main power to be turned off and signal transmission over the device ports to cease. Auxiliary power is provided in the device to monitor the device ports for incoming signals; and on detection of a signal at a port that was previously inactive, main power is restored in the device. Thus having powered down, the device powers up again automatically if a signal appears at a previously inactive port. Ports that were active when the device powered off and remain active should not cause the device to power back on. The signals at those ports must first be detected as absent before any subsequent present signal at those ports may be used to power the device back on. Thus it is only the transition from a signal being detected as absent to a signal being detected as present that can cause a device to power back on.
It is preferred that where there are a plurality of controlling data processing systems in the chain, a shutdown command is issued from one of the host data processing systems only on a determination that the other host data processing systems will not be adversely affected by the shutdown e.g. are either inactive or aware of the shutdown.
The present invention may advantageously be employed in serial communication systems employing protocols such as FC-AL or SSA but it is not limited to such systems. It may be used in any system where each device communicates directly only with an adjacent device. The exact nature of the link between the devices, whether serial or parallel, and the communication protocol employed are not central to the present invention.
The chain configuration of the devices and controlling data processing system(s) may take the form of a string or of a loop.